The present invention relates to a tire having a rubber tread of a lug and groove configuration and of a co-extruded cap/base construction; wherein the tread cap is of a rubber composition which contains carbon black and is thereby of a black color; wherein a visible surface of at least one groove is of a rubber composition exclusive of carbon black and is of a non-black color and wherein said visible non-black colored rubber composition is a rubber layer which underlies said tread cap. Said visible non-black colored rubber is exclusive of any appreciable portion of, and preferably exclusive of, the surface of said tread lugs intended to be ground-contacting. In one aspect of the invention, said non-black colored rubber composition contains an amorphous precipitated silica reinforcement, preferably a pre-hydrophobated precipitated silica. In another aspect of the invention, said non-black colored rubber composition, and alternately, carbon black containing black colored rubber compositions adjoining said non-black colored rubber composition, is comprised a blend of at least one diene based elastomer and a brominated copolymer of isobutylene and p-methylstyrene together with an organo phosphite.
Tires are typically provided with treads which contain carbon black reinforcement and which are therefore black in color.
Most tires have a rubber tread of a lug and groove configuration. Many tires are of a co-extruded cap/base construction, wherein the tread cap is an outer rubber layer which contains the lug and groove configuration for which the outer surfaces of the lugs are designed to be ground-contacting, and wherein the tread base is integral with and underlies the tread cap and is not normally intended to be ground-contacting. Such cap/base tire construction and such tread lug and groove configuration are well known to those having skill in such art.
It is appreciated that, for some tire treads, the tread lugs are in a form of individual lugs and may also be in a form of circumferential ribs. For the purposes of this invention tread lugs and ribs are referred to herein as tread lugs unless otherwise indicated.
Historically, it has sometimes been desirable to provide a tire with a tread of which at least a portion is of a non-black color so that the resulting tread is of a multiplicity of colors, namely black and at least one non-black color.
However, a significant disadvantage of tire treads having a non-black colored outer tread lug surface designed to be ground-contacting is:
(A) a tendency of such non-black colored tread lug surfaces to leave colored markings on the road over which they travel, which can conflict with and confuse colored road markings intended to aid or control vehicular traffic patterns and
(B) a tendency of the such non-black colored tread lug surfaces to become discolored, particularly unevenly discolored, as the outer surface of the tread lugs travel over, or are parked on, oily ground surfaces such as, for example, asphalt roads.
However, it sometimes still remains desirable to provide a tire with a tread of which at least a portion of the visible tread surface has a color which contrasts with the primary black color of the tire tread.
For purposes of this invention, it is intended to provide a black-colored tread of lug and groove configuration which is further configured with at least a portion of the visible surface of at least one of said tread grooves is of a non-black color, preferably a color which contrasts with black, and is of an integral rubber composition which is not carbon black reinforced, namely a rubber composition which is co-extruded with and co-vulcanized with the remainder of the tire tread and is therefore integral therewith.
Thus it is desired that the visible portion of the tire tread is of at least two different visible colors, namely black and at least one additional non-black color which is positioned as a visible portion of least one of said tread grooves and is essentially exclusive of the outer surface of any lug associated with, or a part of, said groove, which is intended to be ground-contacting.
In particular, for the purposes of this invention, such non-black colored, visible groove surface is reinforced with a particulate synthetic amorphous silica and is exclusive of carbon black. Preferably it is also exclusive of any appreciable amount of white colored titanium dioxide pigment.
Accordingly, for this invention, it is desired to provide a black-colored, carbon black reinforced tire tread with at least portion of the visible tread surface being of an integral, non-black colored rubber composition designed to have minimal, in any, contact with the road therefore having minimal, if any, effect upon the wear and traction characteristics of the tire tread. This is accomplished by substantially limiting the non-black colored component of the black-colored tire tread to one or more of the grooves of a tire tread having a lug and groove configuration.
Historically, for a tire tread of cap/base construction which is composed of lugs and grooves, it has previously been proposed to provide such a tread where a portion of the underlying tread base rubber composition extends through the tread cap and is exposed at the surface of the bottom of the tread grooves with a purpose of retarding, or preventing, rubber cracking at the bottom of the tread grooves. For example, see U.S. Pat. No. 5,397,616. However, a visibly multicolored tire tread is not seen to be contemplated.
Also, historically, a typical example of a component of a tire having a color which contrasts with the conventional black color of the tire is a tire sidewall in which a portion of the rubber is white in color resulting from a blend of rubber and titanium dioxide pigment in the absence of, or exclusive of, particulate carbon black reinforcement. Indeed, tires with white colored portions of their sidewalls are well known.
However, for tire treads, it is also appreciated that coloring pigments such as titanium dioxide, by itself, do not provide significant rubber reinforcement equivalent to rubber reinforcing carbon black. Therefore, such white colored tire components are conventionally limited to rubber compositions which do not need such a high degree of reinforcement such as for example, outer, visible, portions of tire sidewalls.
It is also appreciated that many non-black colored rubber compositions for tire components, particularly white sidewall components have a tendency to discolor as a result of various discoloring chemicals which may be contained in various rubber compositions which are adjacent to the colored rubber composition. Accordingly, it is a common practice to substitute non-discoloring chemicals for discoloring chemicals in such adjacent rubber compositions such as for example, non-discoloring antidegradants and non-discoloring rubber processing oils. Such practice is well known in the tire white sidewall art.
A coupling agent is often used for silica-containing rubber compositions to aid in enabling the silica to reinforce the rubber composition. Widely used coupling agents for such purpose are comprised of a moiety (e.g. an alkoxysilane moiety) which is reactive with hydroxyl groups (e.g. silanol groups) on the surface of the silica and another moiety (e.g. a polysulfide moiety) which is interactive with unsaturated elastomers which contain carbon-to-carbon double bonds in their elastomer backbone. Such silica coupling agent activity is believed to be well known to those skilled in such art.
However, if it is contemplated that a saturated elastomer be used, which inherently does not have carbon-to-carbon double bonds in its backbone, such as a halogenated (e.g. brominated) copolymer of isobutylene and p-methyl styrene, such elastomer does not inherently respond to sulfur bonding or crosslinking in the manner of unsaturated diene-based elastomers.
Accordingly, coupling agents for the silica which rely upon an interaction with diene-based elastomers which contain carbon-to-carbon double bonds unsaturation in their backbone, namely polysulfide based couplers such as, for example bis(3-alkoxysilylalkyl) polysulfides, are considered herein to have limited value for coupling the silica to the elastomer, even when the rubber composition also contains a diene hydrocarbon based elastomer, wherein the rubber composition has an appreciable amount of an elastomeric brominated copolymer of isobutylene and p-methyl styrene.
In practice, the aforesaid saturated halogenated copolymer elastomer might be prepared, for example, by first copolymerizing isobutylene and p-methyl styrene. Usually a ratio of isobutylene to p-methyl styrene in a range of about 50/1 to about 7/1 is used. The resulting copolymer is then halogenated with a halogen such as bromine which occurs at the paramethyl position, yielding a benzyl bromide functionality. The degree of bromination can typically be varied from about 0.5 to about 2.5, usually preferably about 1.5 to about 2.5, weight percent, based upon the copolymer of isobutylene and p-methyl styrene.
The following reference provides additional information relating to the preparation of such halogenated copolymers: xe2x80x9cA New Isobutylene Copolymer; Non-tire Usesxe2x80x9d by D. Kruse and J. Fusco, Rubber and Plastics News, Feb. 1, 1993.
Such brominated copolymer of isobutylene and p-methyl styrene may, for example, have physical properties such as, for example, a Mooney viscosity value ML(1+8) at 125xc2x0 C.) in a range of about 35 to about 60 and a Tg in a range of about xe2x88x9250xc2x0 C. to about xe2x88x9260xc2x0 C.
It is to be appreciated that such halogenated (e.g. brominated) copolymer elastomer has a completely saturated backbone as being devoid of carbon-to-carbon double bond unsaturation and therefore is uniquely useful for a rubber composition where stability of various of its physical properties desired when the rubber composition is exposed to atmospheric conditions which conventionally attack unsaturated diene-based elastomers and particularly oxidative influences of ozone.
However, the utility for such halogenated saturated elastomers is limited because, as hereinbefore discussed, because of its lack of carbon-to-carbon double bonds, it is not considered as being reactive with sulfur and is therefore not ordinarily considered as being sulfur curable in a sense of diene hydrocarbon-based elastomers.
Historically, some organo phosphites have previously been recognized as being reactive with alkyl halides. For example, see Introduction to Organic Chemistry, 2nd Edition, by A. Steitwieser, Jr., and C. H. Heathcock, Page 829, which refers to a Arbuzov-Michaelis reaction of a phosphite with an alkyl halide.
It is contemplated herein to apply such indicated alkyl halide activity of organo phosphites for enhancing the utilization of silica reinforcement of rubber compositions which contain a halogenated copolymer of isobutylene and p-methyl styrene.
In the description of this invention, the terms xe2x80x9crubberxe2x80x9d and xe2x80x9celastomerxe2x80x9d if used herein, may be used interchangeably, unless otherwise prescribed. The terms xe2x80x9crubber compositionxe2x80x9d, xe2x80x9ccompounded rubberxe2x80x9d and xe2x80x9crubber compoundxe2x80x9d, if used herein, are used interchangeably to refer to xe2x80x9crubber which has been blended or mixed with various ingredients and materialsxe2x80x9d and such terms are well known to those having skill in the rubber mixing or rubber compounding art.
In the description of this invention, the term xe2x80x9cphrxe2x80x9d refers to parts of a respective material per 100 parts by weight of rubber, or elastomer. The terms xe2x80x9crubberxe2x80x9d and xe2x80x9celastomerxe2x80x9d may be used interchangeably unless otherwise indicated. The terms xe2x80x9ccurexe2x80x9d and xe2x80x9cvulcanizexe2x80x9d may be used interchangeably unless otherwise indicated.
In accordance with this invention, a tire having a rubber tread configured with lugs and grooves wherein the walls of said grooves are also the walls of lugs associated with said grooves, wherein the outer surfaces of at least a portion of said lugs, exclusive of said walls, are designed to be ground-contacting; wherein said tread is comprised of a carbon black-containing, black-colored rubber composition, wherein:
(A) said rubber tread contains a non-black colored rubber layer co-extruded with said tread cap layer wherein said non-black colored rubber layer extends to a visible surface of a wall of at least one of said tread grooves, exclusive of any appreciable portion of, preferably exclusive of, an outer surface of a black-colored tread lug designed to be ground-contacting wherein said tread groove wall is also the wall of said tread lug, and wherein said non-black colored rubber layer is
(1) a non-black colored rubber layer co-extruded with and underlying said tread and comprised of a rubber composition which contains a colorant other than black and is exclusive of carbon black, or
(2) an intermediate non-black colored rubber layer positioned between and co-extruded with said tread and a tread base layer, wherein said intermediate rubber layer is comprised of a rubber composition which contains a colorant other than black and is exclusive of carbon black and wherein said tread base layer is a carbon black containing, black-colored, rubber composition; and wherein
(B) said non-black colored rubber layer is comprised of
(1) 100 phr of elastomer comprised of
(a) about 20 to about 100 phr of at least one diene-based elastomer and
(b) from zero to about 80 phr of a halogenated copolymer of isobutylene and p-methyl styrene, wherein said halogen is selected from bromine or chlorine, preferably bromine,
(2) about 25 to about 100 phr of silica comprised of particulate synthetic amorphous silica selected from at least one of
(a) aggregates of precipitated silica having hydroxyl groups (e.g. silanol groups) on the surface thereof, and
(b) pre-hydrophobated aggregates of precipitated silica having been pre-hydrophobated by treating silica in an aqueous colloidal form thereof with an alkylsilane or with both an organomercaptosilane and an alkylsilane in a weight ratio of said organomercaptosilane to said alkylsilane in a range of from 10/90 to 90/10;
wherein said alkylsilane is of the general Formula (I)
Xnxe2x80x94Sixe2x80x94R4xe2x88x92nxe2x80x83xe2x80x83(I)
xe2x80x83wherein R is an alkyl radical having from one to 18 carbon atoms, n is a value of from 1 to 3 and X is a radical selected from chlorine or bromine or alkoxy radical as (OR1)xe2x80x94, wherein R1 is an alkyl radical selected from methyl and ethyl radicals, and where said organomercaptosilane is of the general formula (II):
(X)n(R2O)3xe2x88x92nxe2x80x94Sixe2x80x94R3xe2x80x94SHxe2x80x83xe2x80x83(II)
xe2x80x83wherein X is a radical selected from chlorine, bromine, and alkyl radicals having from one to 16 carbon atoms; wherein R2 is an alkyl radical having from one to 16 carbon atoms and R3 is an alkylene radical having from one to 16 carbon atoms; and n is a value from zero to 3;
(3) from zero to about 15 phr of a coupling agent having a moiety reactive with hydroxyl groups contained on the surface of said aggregates of precipitated silica and another moiety interactive with said diene-based elastomer(s);
(4) from zero to 20 phr of at least one organo phosphite, or from 0.5 to 20 phr of at least one organo phosphite where said elastomer includes said halogenated copolymer, wherein said organo phosphite is selected from monophosphites selected from formula (III) and diphosphites selected from formula (IV) and diisodecyl pentearythritol diphosphite, distearyl pentaerythritol diphosphite and pentearythritol diphosphite, preferably monophosphites of formula (III): 
wherein each R4 radical is independently selected from alkyl radicals and phenyl radicals and alkyl substituted phenyl radicals; wherein said R4 alkyl radicals have from 1 to 18 carbon atoms, wherein R5 is a phenyl radical; and wherein R6 is selected from alkyl radicals having from 2 to 8 carbon atoms;
wherein said organo phosphite is provided by one or more of the following:
(a) by mixing said organo phosphite with said elastomer(s) and said synthetic silica in an internal rubber mixer,
(b) by pre-reacting said halogenated copolymer of isobutylene and p-methyl styrene with said organo phosphite prior to blending said reinforcing filler therewith,
(c) by pre-reacting said organo phosphite with an aqueous dispersion of colloidal silica particles from which a precipitated silica is recovered to form an organo phosphite/silica composite thereof,
(d) mixing said organo phosphite with said elastomer(s) and said synthetic silica, preferably in an internal rubber mixer, according to any of said steps (a), (b) or (c), wherein said synthetic silica includes at least one of said pre-hydrophobated silica aggregates which has been pre-hydrophobated prior to mixing with said elastomers,
(e) mixing said organo phosphite with said elastomer(s) and an alkylsilane of the said Formula (I) with said elastomer(s) and said synthetic silica, preferably in an internal rubber mixer, and
(f) by pre-reacting said organo phosphite and said alkylsilane of Formula (I) with
(i) said aggregates of synthetic precipitated silica or
(ii) an aqueous dispersion of colloidal silica particles from which a precipitated silica is recovered to form a silica composite thereof.
In one aspect of the invention, a tire is provided having a rubber tread configured with lugs and grooves wherein a portion of said grooves are of a non-black color and are exclusive of carbon black and wherein the faces of said lugs are designed to ground-contacting, contain carbon black and are thereby of a black color, wherein:
(A) said rubber tread contains a non-black colored, silica reinforced, rubber layer, exclusive of carbon black, underlying said groove faces, which extends to a visible bottom of at least one of said tread grooves and is thereby exclusive of any appreciable portion of said lug face and wherein said non-black colored rubber layer is either
(1) a tread base rubber layer co-extruded with and underlying a carbon black containing, black-colored tread cap layer, or
(2) an intermediate rubber layer positioned between and co-extruded with said tread cap layer and a black colored, carbon black-containing tread base layer, and wherein
(B) said non-black colored rubber layer is comprised of
(1) 100 phr of elastomer comprised of
(a) about 20 to about 100 phr of at least one diene-based elastomer and
(b) from zero to about 80 phr of a halogenated copolymer of isobutylene and p-methyl styrene, wherein said halogen is selected from bromine or chlorine,
(2) about 25 to about 100 phr of silica comprised of aggregates of synthetic amorphous silica which contains hydroxyl groups (e.g. silanol groups) on its surface, and
(3) a coupling agent having a moiety reactive with hydroxyl groups on the surface of said silica aggregates and another moiety interactive with at least one of said elastomers.
In one aspect of the invention, said non-black colored rubber layer is comprised of
(A) 100 phr of elastomer comprised of
(1) about 20 to about 100 phr of at least one diene-based elastomer and
(2) from zero to about 80 phr of a halogenated copolymer of isobutylene and p-methyl styrene, wherein said halogen is bromine or chlorine,
(B) about 25 to about 100 phr of silica comprised of aggregates of synthetic amorphous silica selected from at least one of
(1) aggregates of precipitated silica having hydroxyl groups (e.g. silanol groups) on the surface thereof, and
(2) pre-hydrophobated aggregates of precipitated silica having been pre-hydrophobated by treating silica in an aqueous colloidal form thereof with an alkylsilane or with both an organomercaptosilane and an alkylsilane in a weight ratio of said organomercaptosilane to said alkylsilane in a range of from 10/90 to 90/10;
wherein said alkylsilane is of the general Formula (I)
Xnxe2x80x94Sixe2x80x94R4xe2x88x92nxe2x80x83xe2x80x83(I)
wherein R is an alkyl radical having from one to 18 carbon atoms, n is a value of from 1 to 3 and X is a radical selected from chlorine or bromine or alkoxy radical as (OR1)xe2x80x94, wherein R1 is an alkyl radical selected from methyl and ethyl radicals, and where said organomercaptosilane is of the general formula (II):
(X)n(R2O)3xe2x88x92nxe2x80x94Sixe2x80x94R3xe2x80x94SHxe2x80x83xe2x80x83(II)
wherein X is a radical selected from chlorine, bromine, and alkyl radicals having from one to 16 carbon atoms; wherein R2 is an alkyl radical having from one to 16 carbon atoms and R3 is an alkylene radical having from one to 16 carbon atoms; and n is a value from zero to 3;
(3) from zero to about 15 phr of a coupling agent having a moiety reactive with hydroxyl groups contained on the surface of said aggregates of precipitated silica and another moiety interactive with said diene-based elastomer(s);
(4) from zero to 20 phr of at least one organo phosphite, or from 0.5 to 20 phr of at least one organo phosphite, where said elastomer includes said halogenated copolymer, wherein said organo phosphite is selected from monophosphites selected from formula (III) and diphosphites selected from formula (IV) and diisodecyl pentearythritol diphosphite, distearyl pentaerythritol diphosphite and pentearythritol diphosphite, preferably monophosphites of formula (III): 
wherein each R4 radical is independently selected from alkyl radicals and phenyl radicals and alkyl substituted phenyl radicals; wherein said R4 alkyl radicals have from 1 to 18 carbon atoms, wherein R5 is a phenyl radical; and wherein R6 is selected from alkyl radicals having from 2 to 8 carbon atoms;
wherein said organo phosphite is provided by one or more of the following:
(a) by mixing said organo phosphite with said elastomer(s) and said synthetic silica,
(b) by pre-reacting said halogenated copolymer of isobutylene and p-methyl styrene with said organo phosphite prior to blending said reinforcing filler therewith,
(c) by pre-reacting said organo phosphite with an aqueous dispersion of colloidal silica particles from which a precipitated silica is recovered to form an organo phosphitelsilica composite thereof,
(d) mixing said organo phosphite with said elastomer(s) and said synthetic silica, according to any of said steps (a), (b) or (c), wherein said synthetic silica includes at least one of said pre-hydrophobated silica aggregates which has been pre-hydrophobated prior to mixing with said elastomers,
(e) mixing said organo phosphite with said elastomer(s) and an alkylsilane of the said Formula (I) with said elastomer(s) and said synthetic silica, preferably in an internal rubber mixer, and
(f) by pre-reacting said organo phosphite and said alkylsilane of Formula (1) with
(i) said aggregates of synthetic precipitated silica or
(ii) an aqueous dispersion of colloidal silica particles from which a precipitated silica is recovered to form a silica composite thereof.
In the practice of this invention, said coupling agent for said aggregates of precipitated silica may preferably be, for example, an alkoxysilyl polysulfide such as for example, a bis(3-trialkoxysilylalkyl) polysulfide wherein alkyl radicals for said alkoxy groups are selected from one or more of methyl and ethyl radicals, preferably an ethyl radical and the alkyl radical for said silylalkyl component is selected from butyl, propyl and amyl radicals, preferably a propyl radical and wherein said polysulfide component contains from 2 to 8, with an average of from 2 to 2.6 or from 3.5 to 4, sulfur atoms in its polysulfidic bridge.
Representative of such other coupling agents are, for example, bis(3-triethoxysilylpropyl) polysulfide having an average of from 2 to 2.6 or from 3.5 to 4, sulfur atoms in its polysulfidic bridge.
Such coupling agent may, for example, be added directly to the elastomer mixture or may be added as a composite of precipitated silica and such coupling agent formed by treating a precipitated silica therewith or by treating a colloidal silica therewith and precipitating the resulting composite.
In practice, a portion of said non-black colored underlying rubber layer extends to at least one wall of at least one of said tread grooves and preferably includes at least 10 percent, preferably about 20 to about 95 percent, and preferably including the bottom of said groove of said visually exposed groove surface and less than 5 percent of the outer surface of a black-colored tread lug intended to be ground-contacting which is associated with groove, preferably exclusive of said outer surface of said black-colored lug.
In one aspect of the invention, said coupling agent contains a moiety (e.g. at least one alkoxysilyl group) reactive with hydroxyl groups (e.g. silanol groups) contained on the surface of said silica and another moiety (e.g. polysulfide group) interactive with said diene based elastomer(s).
In a further aspect of the invention, said coupling agent may be exclusive of silane based coupling agents and contain a moiety which does not provide an alcohol byproduct upon reaction with said hydroxyl groups (e.g. silanol groups) contained on the surface of said silica.
In another aspect of the invention, said silica is a precipitated silica in a manner that said silica and coupling agent react in situ within the elastomer host.
In a further aspect of the invention, at least a portion of said silica is provided as a pre-hydrophobated precipitated silica in which said silica and coupling agent react in situ within the elastomer host.
In additional accordance with this invention, said tread includes said non-black colored intermediate tread layer and said black colored, carbon black reinforced tread base layer, wherein said tread base layer is not exposed at the surface of the groove and wherein said visually exposed non-black colored tread intermediate layer includes and extends from the bottom of said groove up to at least seventy percent of the distance from the bottom of said groove to the top of said groove. In one aspect of the invention, said visually exposed intermediate layer extends to the top of said groove adjacent to the outer surface of the associated tread lug designed to be road contacting.
Representative of such brominated poly(isobutylene-co-para-methylstyrene) copolymers is Exxpro 3745 from the ExxonMobil Chemical Company. In practice, a purpose of said coupling agent is to aid in enabling said amorphous silica to reinforce the rubber composition, although in a case where said pre-hydrophobated silica inherently contains a coupling agent, use of an additional coupling agent is not believed to be necessary. For example, such coupling agent may be a coupling agent having a moiety reactive with hydroxyl groups contained on the surface of the amorphous silica (e.g. silanol groups) and another moiety interactive with at least one of said diene-based elastomers. Alternatively, said coupling agent may be contained on the silica itself wherein the silica has been pretreated with a coupling agent prior to its addition to the rubber composition.
In practice, the pre-hydrophobated precipitated silica aggregates might be recovered, for example, from said treated colloidal silica, for example as a treated silica hydrosol, with the aid of acid addition to the treated colloidal silica (for example, sulfuric acid or hydrochloric acid) followed by water washing and drying the recovered hydrophobated silica as a hydrophobated silica gel or as a hydrophobated precipitated silica. While this invention is not intended to be directed to a specific preparation technique (preparation of silica hydrosols, recovery of silica gels and precipitated silicas, etc.) of the pre-hydrophobated precipitated silica itself, for education purposes in this regard, reference might be made to the Encyclopedia of Chemical Technology, Fourth Edition (1997), Volume 21, Kirk-Othmer in Pages 1020 through 1026 and U.S. Pat. No. 5,094,829 as well as U.S. Pat. Nos. 5,708,069, 5,789,514 and 5,750,610 for a more detailed discussion.
Representative alkylsilanes of Formula (I) are, for example, trichloro methyl silane, dichloro dimethyl silane, chloro trimethyl silane, trimethoxy methyl silane, dimethoxy dimethyl silane, methoxy trimethyl silane, trimethoxy propyl silane, trimethoxy octyl silane, trimethoxy hexadecyl silane, dimethoxy dipropyl silane, triethoxy methyl silane, triethoxy propyl silane, triethoxy octyl silane, and diethoxy dimethyl silane.
Representative examples of organomercaptosilanes of Formula (II), namely organomercaptosilanes are, for example, triethoxy mercaptopropyl silane, trimethoxy mercaptopropyl silane, methyl dimethoxy mercaptopropyl silane, methyl diethoxy mercaptopropyl silane, dimethyl methoxy mercaptopropyl silane, triethoxy mercaptoethyl silane, and tripropoxy mercaptopropyl silane.
Representative examples of organo phosphites understood to be commercially available are, for example, triisodecyl phosphite, trilauryl phosphite, tris(tridecyl) phosphite, diphenyl isooctyl phosphite, diphenyl isodecyl phosphite, phenyl diisodecyl phosphite, triphenyl phosphite, triisononylphenyl phosphite, trimethyl phosphite, triethyl phosphite, tris (2-chloroethyl) phosphite, triisopropyl phosphite, tributyl phosphite, triisooctyl phosphite and tris (2-ethylhexyl) phosphite, as well as tris (2,4-di-t-butylphenyl) phosphite, and bis 2,4,6,tri-t-butylphenyl 2-butyl-2-ethyl-1,3-propanediol phosphite; and diphosphites as, for example, distearyl pentaerythritol diphosphite, bis (2,4-di-t-butylphenyl) pentaerythritol diphosphite, bis (2,6,di,t-butyl-4-methylphenyl pentaerythritol diphosphite, bis (2,4-dicumylphenyl) pentaerythritol diphosphite and mixtures thereof.
Such organo phosphite may be, for example, tris (2-ethylhexyl) phosphite or triphenyl phosphite.
It is preferred that an in situ reaction of said organo phosphite and silica, optionally including the alkylsilane of formula (I), within the elastomer host may be accomplished without an evolution of an alcohol as compared to using the aforesaid alkoxysilyl polysulfide coupling agent by the inherent chemistry of the organo phosphite material and hydroxyl groups contained on the surface of said silica material in which water evolved instead of an alcohol as a byproduct of the reaction.
In the further practice of the invention, the aforesaid in situ reaction of said organo phosphite silica material within the elastomer host via said internal rubber mixing process is accomplished wherein said silica material is a precipitated silica and/or silica-containing carbon black which is hydrophobated prior to its addition to the elastomer (pre-hydrophobated). Such in situ reaction is considered herein to be important as to both the process of mixing and reacting of the organo phosphite and pre-hydrophobated silica material as to a resulting product thereof. In particular, is it considered herein that pre-hydrophobation of the silica material, particularly with an alkyl silane of the general formula (I) enables a more efficient mixing, or processing, of it within the elastomer host in that such pre-hydrophobation of the silica material
(A) renders it more compatible with the diene-based elastomer and
(B) substantially reduces a tendency for a precipitated silica to agglomerate with itself within the elastomer host.
In the practice of this invention, said pre-hydrophobated precipitated silica aggregates may be pre-hydrophobated, for example, by treating silica in an aqueous colloidal form thereof with said alkylsilane of Formula (I).
In another aspect of the invention, said elastomer composition for said non-black colored tread rubber layer(s) and for rubber composition(s) in direct contact with said non-black colored tread rubber layer(s) of is preferably devoid of rubber processing oil other than paraffinic rubber processing oils which contains less than 8 weight percent aromatic compounds and is preferably devoid of antidegradants other than phenolic antidegradants.
In practice, said non-black colored rubber composition may be prepared, for example, by mixing in at least one sequential preparatory (non-productive) blending step in at least one internal rubber mixer to a temperature in a range of about 100xc2x0 C. to about 180xc2x0 C. a blend of said elastomer(s) with said synthetic amorphous silica and/or pre-hydrophobated silica, normally in the absence of sulfur curative, followed by blending the mixture thereof with sulfur curative(s) in a subsequent (productive) blending step in an internal rubber mixer to a temperature in a range of about 95xc2x0 C. to about 115xc2x0 C.
In practice, in the case of using the synthetic amorphous silica, a coupling agent may be added in one or more non-productive (preparatory) mixing steps or divided into an addition in a non-productive (preparatory) mixing step and in a productive mixing step together with the sulfur curative.
The reaction of such coupling agent with the hydroxyl groups on the surface of the silica yields an alcohol such as, for example, ethanol during the manufacture of various silica reinforced rubber products. If such evolution of materials other than alcohol in the manufacture of rubber products would be desired, coupling agents which release water instead of alcohol might be used.